1. Field of the Invention
The present invention relates to an ignition transformer for gas discharge bulbs or tubes.
Although the present invention is concerned primarily with gas discharge bulbs for vehicle headlamps, it is not restricted solely to such use.
2. Description of the Related Art
One problem with a gas discharge bulb, or tube, is that ionization of the gas in the bulb, and therewith ignition of the bulb, or tube, requires the application of a high voltage while a much lower voltage is required in operation, for instance an alternating voltage of from 65-105 V. The combination of a high ignition voltage and a low operating voltage with a high current strength during operation constitutes a well known problem.
It is difficult to generate a voltage that is high enough to give positive ignition and, at the same time, achieve high operating efficiencies by using one and the same circuit for both ignition and operating purposes.
Parallel connection of an ignition transformer with the drive circuit presents the problem of insulating and protecting the drive circuit with respect to the ignition pulse, and also presents problems with regard to switching from an ignition mode quickly enough to prevent the bulb from being extinguished.
Connection of the ignition transformer in series between the bulb and the drive circuit presents the problem of combining a high ignition voltage, which requires many winding turns, with a low impedance in the operating mode which requires few winding turns and/or the use of heavy gauge winding wire. Because the ignition voltage is as high as 20-30 kV, there is a significant risk of oversparking arid large insulation thicknesses are required. The requirement of small dimensions and low weight make these problems large problems.
These problems are solved by the present invention.